A metal leadframe is one of the components of a semiconductor device. Leads of the leadframe must be arranged at finer pitches to provide a higher pin-count package. The strength of leads decreases when the width of the leads is reduced according to the reduction of lead pitches. Consequently, the leads are bent or deformed, causing short circuits. Therefore, the semiconductor device is packaged inevitably in a large package to arrange leads at proper pitches. Thus, a package containing a semiconductor device including a leadframe is large and thick. Accordingly, surface-mount semiconductor devices of leadless construction not subject to restrictions placed by the leadframe have been proposed in, for example, Patents 1 and 2.
Patent 1: JP-A 9-252014
Patent 2: JP-A 2001-210743
FIGS. 7(a) and 7(b) show a semiconductor device mentioned in Patent 1. A method of fabricating this semiconductor device affixes a metal foil to a base 101, processes the metal foil by an etching process to leave predetermined parts of the metal foil, and bonds a semiconductor chip 102 to a part 103a, i.e., a die pad, of the metal foil with an adhesive layer 104. The method connects the semiconductor chip 102 electrically to parts 103b of the metal foil with wires 105, and packages the semiconductor chip 102, the metal foil and the wires 105 in a sealing resin molding 106 by transfer molding as shown in FIG. 7(a). The method separates the sealing resin molding 106 from the base 101 to complete a semiconductor device, i.e., a semiconductor IC package, as shown in FIG. 7(b). Since the semiconductor device fabricated by this method includes, in addition to the semiconductor chip 102, the adhesive layer 104 and the part 103a (die pad) of the metal foil, the problem is forming the semiconductor device in a small thickness.
The semiconductor device fabricating method mentioned in Patent 1 requires the metal foil to adhere closely to the base for an etching process for etching the metal foil and a molding process for sealing the semiconductor chip in the resin molding, and requires the metal foil and the sealing resin package to be easily separated from the base after the molding process. Thus, the base and the metal foil are required to have contradictory adhesive characteristics. Whereas the material bonding the metal foil to the base must be resistant to the etching action of the etching solution and the semiconductor chip must be held in place against pressure that acts thereon when the hot sealing resin flows into the mold during the molding process, the sealing resin package and the metal foil must be easily separated from the base. However, a base formed of Teflon® or a base formed of a metal and coated with silicone or Teflon® is utterly unable to have such an adhesive characteristic.
FIGS. 8(a) and 8(b) show a semiconductor device mentioned in Patent 2. The following semiconductor device fabricating method is used to fabricate this semiconductor device. A metal plate 201 provided with grooves 201 formed in a grid is formed. A semiconductor chip 202 is bonded to the metal plate 201 with an adhesive layer 203. Wires 204 are extended by wire bonding between design parts. A sealing resin molding 205 is formed by transfer molding as shown in FIG. 8(a). Then, the metal plate 201 and the adhesive layer 203 are ground to shape the metal plate 201 and the sealing resin molding 205 in a design size to complete a semiconductor device as shown in FIG. 8(b). The semiconductor device fabricated by this semiconductor device fabricating method, however, includes the adhesive layer 203 and the metal plate 201 accompanying the semiconductor chip 202. Such construction of the semiconductor device is a drawback in providing thin semiconductor devices desired by the industry.
Thus, the conventional semiconductor device fabricating methods have difficulty in fabricating a thin semiconductor device. Therefore, the semiconductor chip needs to be formed in a small thickness by grinding to form a thin semiconductor device. Thin semiconductor chips are liable to be chipped or cracked in semiconductor device fabricating processes, and defective semiconductor chips increases the cost of semiconductor devices. Use of the adhesive needs additional processes and additional materials, which also increases the cost of semiconductor devices.